Analysis of transients for NPP with VVER-440 using the code SiTAP

The report contains results of the analysis of the transients "Loop connection" and "SG tube rupture" for NPP with VVER-440 type reactors. To obtain detailled informations about NPP's dynamic characteristics, various variants of initial and boundary conditions are considered. Calculation of these transients was performed with use of the code SiTAP developed at the Nuclear Safety Institute of Russian Research Centre "Kurchatov Institute". SiTAP is a multi-functional computer tool for fast analysis of transient and accidental processes of VVER type reactors for engineers working in the field of NPP dynamics. SiTAP can be used for comparative analysis of several variants of accident scenarios to find out the conditions leading to the most severe consequences from safety point of view. For this cases, additional analyses using best-estimate codes should be carried out. The results from SiTAP for faulty loop connection leading to a boron dilution accident are intended to be used as boundary conditions for a more detailled analysis by the help of the three-dimensional reactor core model DYN3D, developed in the Research Centre Rossendorf for the simulation of reactivity initiated accidents

Experience of the application of pedagogical control as a way of diagnosing the effectiveness of students 'academic activity at the department of medical and bioorganic chemistry at KHNMU

У статті на основі аналізу літературних джерел вказується на значення правильної організації і управління навчально-пізнавальною діяльністю студентів- медиків та роль у цьому процесі одної з важливих складових - педагогічного контролю. Автори діляться досвідом застосування педагогічного контролю при вивченні хімічних дисциплін на своїй кафедрі: наголошують на значенні контролюючих заходів різних форм як засобу діагностування стану навчальної роботи для студентів і для викладачів.Based on the analysis of literary sources, the article indicates the importance of the proper organization and management of educational and cognitive activities of medical students and the role in this process of one of the important components - pedagogical control. The authors share their experiences with use of pedagogical control in the study of chemical disciplines at their department: they emphasize the importance of monitoring activities of various forms as a way of diagnosing the state of academic work for students and teachers

Non-Magnetic Spinguides and Spin Transport in Semiconductors

We propose the idea of a "spinguide", i.e. the semiconductor channel which is surrounded with walls from the diluted magnetic semiconductor (DMS) with the giant Zeeman splitting which are transparent for electrons with the one spin polarization only. These spinguides may serve as sources of a spin-polarized current in non-magnetic conductors, ultrafast switches of a spin polarization of an electric current and, long distances transmission facilities of a spin polarization (transmission distances can exceed a spin-flip length). The selective transparence of walls leads to new size effects in transport.Comment: 4 pages, 2 figure

Angle-Resolved Spectroscopy of Electron-Electron Scattering in a 2D System

Electron-beam propagation experiments have been used to determine the energy and angle dependence of electron-electron (ee) scattering a two-dimensional electron gas (2DEG) in a very direct manner by a new spectroscopy method. The experimental results are in good agreement with recent theories and provide direct evidence for the differences between ee-scattering in a 2DEG as compared with 3D systems. Most conspicuous is the increased importance of small-angle scattering in a 2D system, resulting in a reduced (but energy-dependent) broadening of the electron beam.Comment: 4 pages, 4 figure

A Magnetic-Field-Effect Transistor and Spin Transport

A magnetic-field-effect transistor is proposed that generates a spin-polarized current and exhibits a giant negative magnetoresitance. The device consists of a nonmagnetic conducting channel (wire or strip) wrapped, or sandwiched, by a grounded magnetic shell. The process underlying the operation of the device is the withdrawal of one of the spin components from the channel, and its dissipation through the grounded boundaries of the magnetic shell, resulting in a spin-polarized current in the nonmagnetic channel. The device may generate an almost fully spin-polarized current, and a giant negative magnetoresistance effect is predicted.Comment: 4 pages, 3 figure

Single-electron shuttle based on electron spin

A nanoelectromechanical device based on magnetic exchange forces and electron spin flips induced by a weak external magnetic field is suggested. It is shown that this device can operate as a new type of single-electron "shuttle" in the Coulomb blockade regime of electron transport

The electrical resistance of spatially varied magnetic interface. The role of normal scattering

We investigate the diffusive electron transport in conductors with spatially inhomogeneous magnetic properties taking into account both impurity and normal scattering. It is found that the additional interface resistance that arises due to the magnetic inhomogeneity depends essentially on their spatial characteristics. The resistance is proportional to the spin flip time in the case when the magnetic properties of the conducting system vary smoothly enough along the sample. It can be used to direct experimental investigation of spin flip processes. In the opposite case, when magnetic characteristics are varied sharply, the additional resistance depends essentially on the difference of magnetic properties of the sides far from the interface region. The resistance increases as the frequency of the electron-electron scattering increases. We consider also two types of smooth interfaces: (i) between fully spin-polarized magnetics and usual magnetic (or non-magnetic) conductors, and (ii) between two fully oppositely polarized magnetic conductors. It is shown that the interface resistance is very sensitive to appearing of the fully spin-polarized state under the applied external field

Loop cosmology: regularization vs. quantization

It is argued that it is the regularization of the classical Hamiltonian —the first step in loop cosmology in order to build a well-defined quantum theory— that is already able to avoid the Big Bang and Big Rip singularities, rather than the usually invoked quantum corrections coming from the quantization of the Hamiltonian. To prove such statement, the classical regularized Hamiltonian corresponding to loop gravity is obtained, and it is shown that it coincides, up to terms of order planck, with the so-called effective Hamiltonian which is calculated from the quantum regularized Hamiltonian using semi-classical techniques. From that comparison it is concluded that both types of singularities are avoided at the "classical level" already, i.e., using loop cosmology, in the sense that only the quantum nature of the geometry is invoked (the loop cut-off) in order to construct the regularized Hamiltonian and to fix the parameter on which it depends. Such finding constitutes a key manifestation of the intrinsic power of loop gravity, as compared with other alternatives